Inductance coil and method of making such coils



Feb. y17, 1959 M. H. BROWN 2,874,361

INDUCTANCE COIL AND METHOD OF MAKING SUCH COILS Filed July 22, 1955 2 :sheets-sheetv 1 Feb..v 17, 1959 M. H. BROWN 2,874,361

` INDUCTANCE conJ AND METHQD oF MAKING SUCH coms Filed July 22, 1955 7g il zg 2 Sheets-Sheet 2 United States Patent O IN DUCTANCE 'COIL AND METHOD OF MAKING SUCH COILS Maurice H. Brown, Palos Heights, Ill., assignor to Oaktron Electric Company, Tinley Park, Ill., a corporation of Illinois Application July 22, 1955, Serial No. 523,850 Claims. (Cl. 336-209) The present invention relates to a novel type of inductance coil and to a method for making such coils.

One of the objects of the present invention is to provide a novel inductance coil of pancake type which has superior physical and electrical properties.

Yet another object is to provide a pancake type inductance coil which is suitable for use as the antenna coil in radio receivers and like equipment.

Still another object is to provide an improved radio antenna coil of pancake type which needs no backing panel or other support since the coil itself has a high order of physical strength.

Still another object is to provide a novel coil of this type which may be supplied in circular form or in the more usually used oval or generally rectangular form with rounded corners, but which can be wound upon a cylindrical mandrel and subsequently shaped to the desired configuration.

Still another object is to provide a coil of the above type and method for producing such a coil which results in pancake coils having superior electrical and mechanical properties at lower manufacturing costs than has heretofore been possible so far as I am aware.

Yet another object is to provide a novel and improved high Q antenna or similar coil for use in electronic circuits which is self-sustaining, which may be provided in all of the generally used forms, and which may be manufactured at extremely low cost.

Other objects and advantages will appear from the following description of a preferred embodiment of my invention which is illustrated in the accompanying drawings.

In the drawings, in which similar characters of reference refer to similar parts throughout the several views:

Figure l is a diagrammatic representation of the principal portion of a machine for practicing the method of the present invention and for producing pancake coils of the type described above;

Fig. 2 is a vertical transverse sectional view which may be considered as taken in the direction of the arrows, substantially along the line 2 2 of Fig. 1;

Fig. 3 is a view similar to Fig. 2 but taken in the direction of the arrows along the line 3 3 of Fig. l;

Fig. 4 is a vertical transverse sectional view which may be considered as taken in the direction of the arrows along the line 4-4 of Fig. l;

Fig. 5 is a transverse vertical sectional view taken in the direction of the arrows along the line 5-5 of Fig. 1;

Fig. 6 is a view similar to Figs. 2 to 5 but taken in the direction of the arrows along the line 6 6 of Fig. l;

Fig. 7 is a side view of a portion of the apparatus and may be considered as a continuation of Fig. 1 to the left;

Fig. 8 is a view of an individual coil embodying fea tures of the invention after it has been removed from a winding mandrel and binding strips and terminals have been secured thereto;

2,874,361 Patented Feb. 17, 1959 Fig. 9 is a transverse sectional view drawn to larger scale through a portion of the coil of Fig. 8, showing the appearance of the layers of wire and insulating material;

Fig. 10 shows the coil of Fig. 8 after it has been shaped to generally oval form;

Fig. 11 is a fractional perspective view showing the arrangement of the terminals which may form a portion of the pancake coil, with one of the ends of the coil attached thereto; and

Fig. 12 is a View of a coil similar to that shown in Fig. l0 but having a considerably greater ratio of length to width.

The manufacture of radio receiving sets and similar electronic equipment requires the production of large numbers of antenna coils or similar inductances of one shape or another for incorporation into the equipment. Typically, the back cover or one of the fixed walls of a radio cabinet is provided with a pancake type coil for the purposes of providing the antenna and the inductance in the input circuit. These coils vary considerably in overall configuration, depending upon the shape and space limitations of the cabinet. In general they vary from circular through oval to rather long comparatively narrow coils which are essentially rectangular excepting that the corners or ends are well rounded. Such pancake coils have a plurality of radially spaced insulated turns and are only one turn deep in an axial direction. The inductance of these coils varies, depending upon the circuit, but usually must be held to quite close limits. A typical coil of this type for use in a broadcast receiver may have an inductance of about 200 microhenrys as an example.

A typical application of the present invention is to provide coils of this general character.

Probably the most commonly used arrangement for winding antenna coils of the pancake type is to use antenna wire which is insulated with cellulose acetate. The insulated wire is drawn through a solvent and then wound upon a mandrel having an appropriate shape to produce the coil in its final configuration. That is, the winding mandrel for a noncircular coil, such as shown in Figures l0 or l2 for instance, will have the shape of the open center of the coil. The wire with the solvent softened insulation is wound into a narrow slot so that one turn lies on top of another in a radial direction. The softened cellulose acetate bers adhere together and thereby produce a coil having some self-sustaining properties. Such coils are, however, quite weak and tlirnsy and are ordinarily immediately attached to a supporting panel of cardboard, ber, or plywood before being sent from the coil manufacturer to the assembly line.

Coils of this type, as will be readily appreciated, will not retain their form so that they can be taken olf the mandrel, unless adjacent turns adhere together, and therefore the shape of the coil cannot be changed once it has been wound. This is a considerable limitation on the rate of production of noncircular coils, since coils wound in oblong form must be wound slower than circular coils. This is because the rate of supply of wire to the coil form is quite irregular as the noncircular form is rotated.

Another great disadvantage associated with a coil as so made is that it is impossible to hold the inductance within lclose limits, since slight variation in the diameter of the wire insulation will change the manner in which one turn lies on top of another. That is, there will be some sidewise displacement of adjacent turns if the wire diameter is small, even though itis within manufacturing tolerance.

Referring now to Figs. l to 7 of the drawings, l have shown a roll of low cost neutral kraft paper ribbon at supported upon an axle 22 carried by upright side members 24. Typically this paper can be about fourto vethousandths of an inchthick and about three-eighths of an inch wide. The paper stripleading from the coil 20 is indicated at 26 and, as shown, it passes beneath a roller 28 and then is fed between a pair of forming rolls ,30 and 32. These rolls have a configuration such as is shown in Fig. 2, where it will be seen that the lower roll 30 has a rectangular groove 31 in its periphery having approximately the width lof the paper strip 26 with two spaced narrow grooves 34 and 36 in the central portion thereof. These grooves 34-and 36 extend circumferentially and are so spaced that the distance between them in the present instance is approximately one-eighth of an inch.

The top roll 32 is provided with a pair of circumferentially extending ribs 38 and 40 which mesh with the grooves 34 and 36. The spacing between the rolls 30 and 32 may be adjusted so that the paper strip 26 passing between the rolls is provided with two longitudinally extending creases approximately lone-eighth of an inch apart as is best seen in Fig. 2.

' The ribbon 26 next passes between a pair of horizontally journaled rolls 42 and 44. The lowermost roll 42 has a rectangular groove in its periphery approximately oneeighth of an inch wide, and the bottom of this slot is one-eighth of an inch or more from the peripheral surface. The uppermost roll 44 of the set has a complementary edge shape excepting that the central portion 46 of its circumferentially extending rib 48 is grooved to provide a slot 50 through which a length of copper wire 52 may be fed. This slot 50 is slightly deeper at its edges than at its center, so as to provide an obtusely triangular ridge 54 which causes the wire 52 to lie toward either on one side or the other of the central portion of the paper strip 26.

The wire 52 is uninsulated and may in a typical embodiment of the invention be 28 gauge. This wire is fed from a supply coil, not shown, and as is best seen in Fig. 3 it is deposited into the central portion of the U-shaped paper trough near one side thereof. Either automatically or manually, the wire 52 can periodically -be pushed to the opposite side so that it snaps over the ridge 54 and thereafter is fed into the U-shaped paper trough near the other side thereof until it is again purposely moved to the original position. Although this is not essential in practicing the method of the present invention, it does have advantages which will appear presently.

After leaving the rolls 42 and 44, the paper strip 26 passes over the top surface of a longitudinally extending at -shoe 56, and the upwardly extending paper wings indicated at 62 are pressed toward each other by a pair of rollers S8 and 60 which rotate about inclined axes.

After passing the rolls 5S and 60, one of the upstanding wings 62 is bent over and folded approximately flat against the wire and the vcentral portion of the strip by an inclined roll 64 having a conical face. During this operation the central portion of the U-shaped strip is supported by the shoe 56. The relative positions of the wire andthe portions of the paper strip at this juncture are best seen in Fig. 5.

After passing the station at the roll 64 the paper strip with the wire therein passes downwardly over a cylindrical roller at 66. The bending of the paper strip around the portion of the periphery of this roller in contact therewith `causes the top wing 62 to tighten and be drawn down snugly against the underlying layer 62 as is best seen -in Fig. 6. Preferably, after passing the roller 66, the longitudinally folded paper strip with the wire therein is passed between a pair of flat electrically heated ironing shoes 68 and 70 shown in Fig. 7. One of these, for instance the shoe 68, is fixed, whereas the other, 70, is spring loaded toward it so as to exert an ironing pressure upon the paper strip.V These'ironing shoes are helpful in setting the edge creases in the strip, lbut under some circumstances are not necessary.

After emerging from these ironing shoes the folded paper strip with the wire therein will appear much as in Fig. 6 and is passed to a coil Winder which may be of any conventional type so as to be wound into a circular Vcoil 72 which appears as in Fig. 8. All of the rolls mentioned above and shown in Fig. 1 can simply idle, movement of the paper strip and wire being' accomplished by the coil winding mandrel.

The circular coil thus produced will be approximately one-eighth of an inch thick `from front to back and because each of the layers comprising the folded paper strip containing the wire are wide as compared to their thickness, the coil has considerable stiffness. This effect is also enhanced by the reinforcing function of the copper wire.

The coil is secured against unwinding by a suitable means. For instance in Fig. 8 the coil is shown as being wrapped at four places with gummed paper strips 74. At the place where the inner and outer ends 76 and 7S of the coil are opposite to each other, I prefer to place a pair of T-shaped metal terminal members 80 on the inner and outer surfaces of the coil and to secure these terminal strips to the `coil by means of a pair of gummed paper strips 74.

After the terminals are in place, one end of the coil is stripped and wrapped aroundV one of the terminals and soldered thereto, whereas the other end of the coil is similarly attached to the other terminal.

At this juncture, or at any time after the coil has been wound as shown in Fig. 8, it can be pressedrto oval or generally rectangular shape as illustrated'in Figs. l0 and l2, after which l prefer to dip the -coil in a hot wax bath which improves its Q as well as providing a rigid coil which is not readily subject to accidental damage during handling.

In the event that the ratio of the length to the width of the coil is quite great, as illustrated in Fig. 12 for instance, paper binding strips such as indicated at 74 may be desirable in more than four places or, if desired, the coil may be served with thread 79 on a toroidal wrapping machine as is illustrated in Fig. l2. For this purpose I have found that toroidal serving with thread at a pitch of about twenty-five turns per foot, serves the purpose admirably.

Where a coil has a considerable number of turns or where the diameter of the wire is comparatively great, there is a tendency, if the wire is always at one side of the coil, for the coil to become somewhat lopsided because of the greater thickness of the individual turns at one side than at the other due to the additional thickness of the wire. As is best seen in Fig. 9, this can be avoidedby periodically shifting the wire 52 from one side to the other of the central ridge 54 of the roller 44. Conveniently, several turns can be wound with the wire at one side and then the wire 52 can be snapped to the other side of the ridge 54 for several more turns. After being shifted, it takes about one turn for the wire to cross over to the opposite side of the coil in a typical application. This periodic movement of the wire from side to side of the ridge 54 or in fact` such shifting movement with every turn if desired, has the additional advantage of increasing the Q of the coil somewhat by reducing the inter-turn capacity between the wire layers.

An inspection of Fig. 9 will show that the successive turns in the coil are separated from eachother by three layers of paper even when the wire is at the same side of the coil which is better insulation than coils of this general character usually have. The result is that the Q of coils wound in this fashion has been found to be very high, considerably higher than coils ordinarily considered as acceptable for the purpose and wound in the manner previously mentioned. Furthermore, paper is quite uniform and coils wound in this improved manner can be held to closer manufacturing tolerances than is ordinarily practical.

The direct manufacturing cost other than material cost of coils wound in this fashion is considerably less than with coils wound in the customary fashion, both because handling is facilitated due to the inherent rigidity of the coils and further by the fact that all coils are rapidly wound on circular forms and are subsequently quickly and easily shaped to the final specifications. The material cost is also considerably lower since bare uninsulated copper wire and kraft or other paper are much less expensive than is insulated wire.

It has been found that coils fabricated according to the teachings of the present invention can be inserted directly into radio receiving7 sets and similar equipment and simply attached in place suiciently to retain their location without the necessity of providing support for the coil as by a stiff cardboard or thin wood panel.

In the above description of a preferred embodiment of my invention, certain specific dimensions have been used by way of illustration and these specific recitations should not be considered as limitative of the invention. It will be appreciated further that variations may be made in the coils, the method used and the machinery without departing from the scope or spirit of the invention and that the scope of the invention is to be measured by the scope of the following claims.

Having described my invention, what I claim as new and useful and desire to secure by Letters Patent of the United States is:

1. An inductance coil comprised of a plurality of turns of small diameter wire, the turns being mutually insulated by a folded ribbon of insulating material, there being two longitudinally extending fold lines dividing said ribbon substantially into thirds transversely to provide a central section having a width of several times the maximum transverse dimension of the wire and a pair of wing sections of a width substantially equal to that of said central section, said wire lying against said central section and being covered by one of said wings folded thereover and the other of said wings being folded over and covering said one wing, so that said wire is insulated on one side by said central section and on the opposite side by both said wings, whereby adjacent turns in said coil are insulated from each other by three thicknesses of the insulating material of which the ribbon is formed.

2. An inductance coil as called for in claim 1 which has been made substantially rigid by wax impregnation.

3. An inductance coil as called for in claim 1 in which the position of the wire within the folded ribbon enclosure is different in some of the turns from its position in others of the turns.

4. An inductance coil as called for in claim 1 in which the ribbon is formed of paper.

5. The method of making an inductance coil which comprises feeding a ribbon of insulating material, folding said ribbon twice longitudinally to provide a trough having a central section and a pair of marginal wings, feeding a round wire into said trough, folding both of said wings over said wire to enclose said wire, said folded ribbon with the wire therein having a width of several times its thickness, winding said ribbon with the wire therein to form a pancake coil, and securing the turns of said coil together to prevent unwinding of said coil, the position of the wire within said folded ribbon being shifted from side to side periodically during the winding operatori.

References Cited in the le of this patent UNITED STATES PATENTS 748,911 Anderson Jan. 5, 1904 753,461 Anderson Mar. 1, 1904 783,546 Rupley Feb. 28, 1905 1,455,188 Cox May 15, 1923 

